The present invention relates to electro-dynamic transducers such as loudspeakers and in particular to a dynamic equalizer for providing an improved or relatively level transducer output and for simultaneously protecting the transducer against damage through excessive motion or temperatures or fatigue from being overdriven.
There are known transducer driving systems employing one form or another of electric equalization including special amplifiers or feed-back systems which however, have not permitted the systems to achieve their maximum potential in providing a generally level signal output and in obtaining maximum volume for a transducer of a given size without the risk of transducer damage.
The system of the present invention is based upon a recognition that for a level output maximum transducer deflection is required at the low frequency end of the driving signal. It provides for a boost of the low frequency portion of the signal while at the same time providing for a dynamic and frequency sensitive protective means for operating the transducer below destructive levels either for mechanical movement, or temperature, or through fatigue after extended transducer use.
For example, exceeding maximum loudspeaker cone travel results in severe acoustic harmonic distortion at low frequencies as well as very audible intermodulation distortion between the low frequencies and the other higher frequency music waveforms. This problem is avoided in the dynamic equalizer which senses an electrical replica or other sampling of cone travel and reduces the low frequency response of the equalizer when a predetermined peak-inward or peak-outward cone travel is exceeded. Therefore, the loudspeaker system reproduces the electric signals as acoustic signals, reducing the frequency response whenever excessive levels are encountered and distortion and damage are avoided.
The equalizer circuit is designed to be connected between a preamplifier output and the power amplifier input or the tape-monitor circuit of a typical receiver of amplifier. Additionally, the circuit acts as a connection between the loudspeaker output terminals of the power amplifier circuit and the loudspeakers. This connection provides signals for the cone-displacement sensing circuit with the internal circuit permitting both single-ended and bridging mode power amplifier circuits without any other modifications.
The dynamic equalizer may provide two channels of unity gain at mid and high audio frequencies and provides a boost at low frequencies to equalize the frequency response of the loudspeakers. At signal levels below a threshold, a low frequency cutoff of about 40 Hz protects the loudspeakers against sub-sonic and other low frequencies. Beyond threshold, the cutoff or high-pass frequency increases with increasing signal while the low-frequency boost above cutoff is simultaneously reduced. By this means overall flatness of frequency response is maintained with only the low frequency limit increased.
Accordingly, an object of the present invention is to provide an improved system for driving electro-dynamic transducers or speakers.
Another object of the present invention is to provide an improved driving system for speakers providing a generally level audio output.
Another object of the present invention is to provide a speaker driving system which protects the driven speakers against damage from excess signal input particularly at low frequencies.
Another object of the present invention is to provide a relatively simple and inexpensive and reliable system for equalizing the audio output of speakers.
Other and further objects of the present invention will become apparent upon an understanding of the illustrative embodiments about to be described or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.